Method of treating alunite.



APPLICATION FILED JAN. 8,1916.

Patented July 17, 1917.

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4SLALES PATENT OFFICE.

FRANK K. CAMEBQN, 0F WASHINGTON, DISTRICT OF COLU'MZBIA.

METHOD 0F TBEATING ALUNITE.

Specication o! Letters Patent.

Patented July 17, 1917.

Application lcd January 8, 1918. Serial No. 70,973.

provements in Methods of Treating Alunite, of which thefollowing is a specification.

This invention relates to methods of treating alunite or like minerals (alum rock,

alum stone, etc.) for the purpose of producing therefrom, as merchantable prod- ;ucts, otassium sulfate and substantially ure a umma, together with aluminum sulateif desired.

It has been proposed heretofore to calcine "erence to a preferred specific embodiment thereof, reference being made to the accompany-i drawing which illustrates diagrammati y the nature and sequence of the several steps. y 4

The alunite or related mineral 'is rst pulverized, preferably to 10-20 mesh and 1s then calcined at a carefully regulated temperature chosen with the .object of convertin the maximum practicable proportion o the alumina into water-soluble form,

y while avoiding substantial evolution of oxids of sulfur. For this purpose I prefer to use a rotary kiln of the type employed in cement mills, the temperature bein maintained at 500 to 550 C. However I o not desire to be restrictedrftothe use o temperatures within these limit''masmuch as the time of treatment alsoenters as a factor. The heating should not be so lon continued as to drive olf considerable vo umes of the oxids of sulfur.

The lcalcined material is. then treated with water, to which a small proportion ofA sulfuric acid may be added if necessary.'

The resulting mixture is treated in asocalled thickener which may be of the Dorr type, and the alum solution is continuously drawn olf, crystallized out, and the crystals calcined at a materially higher temperature than that to which the original charge was subjected. The urpose of this calcination is to decompose t e alum and toV render its alumina content insoluble; this may be accomplished in a rotary kiln at a temperature of 700 to 7 50 C., the conditions being so chosen as completely to decompose the alum, while liberatin pjracticable proposition of s -fur trioxid.

nder properly regulated conditions approximately 90 per cent. of the total evolved oxis of sulfur may consist of' sulfur tri- 0x1 The crude alumina from which' the alum solution was drawn is transferred to a digcster, to which is also led the gas evolved from the calcination of the alum. The reaction in this digester yields aluminum sulfate, which may either be 'crystallized out and marketed as such, A4or may be crystallized and calcined with the alum, with production ofv alumina and sulfur trioxid.

The calcined material from the high-tem perature kiln consists essentially of potassium sulfate and aluminum oxid. This is mixed with water with thorough agitation, and is passed through a second series of thickeners, from which there is discharged, as a residue, substantiallyr pure alumina, which constitutes one of the merchantahle products of the operation. The solution drawn from these thickeners consists essentally of potassium sulfate, which is crystallized out, the crystals bein freed from mother liquor by filtration or raining, and dried, constituting another merchantable product. The mother liquor from the tassium sulfate crystals may be somew at concentrated by evaporation, and returned to the mixing tank, which as before stated ,receives the charge from the high temperathe highest ture or alum It is preferred, however,

that this mother liquor should be returned to the alum leaching-system, in which, with such additions of water as may be required, it serves to dissolve the alam from the charge from the low-temperature calcination. By proceeding in this way its potassium sulfate contents are'fully conserved, while at the same time the expense of evaporating it is avoided.

It will be understood-that my invention is not restricted to the performance of all of the steps and mampulative processes above described, inasmuch as it is obvious that these may be variously modified Without de arting from the spiritof the invention. lor is the invention restricted to the use of the particular types of apparatus which vhave been described above as well adapted for the I'practice of the method.

It will be understood that alum prepared in the first sta 'e of the process may be marketed as suc' if so desired.

I claim l. A method of treating alunite comprising calcining the same While so regulating 'the temperature and time of treatment as to convert the bulk of the alumina into watersoluble form While avoiding substantial evolution of oxids of sulfur, leaching the calcined material and separating alum from the solution. thereby'obtained, calcining the alum and thereby converting the same into potassium sulfate, alumina, and oxids of sulfur, the latter consisting predominately of sulfur trioxid, extracting and recovering the potassium sulfate, and recovering the residual alumina.

2. A method of treating alunite comprising calcining the same at about 50G-550 C., thereby producing the maximum practicable proportion of soluble aluminum compounds with the minimum evolution of oxids of sulfur, leaching the calcined material and separating alum from the solution thereby obtained, calcining the alum at about TUO-750 C., and thereby converting the same into potassium Sulfate, alumina, and -oxids of sulfur, extracting and recoverlng the potassium sulfate, and recovering the residual alumina.

3. A method of treating alunite comprising calcining the same While so regulating the temperature and time of treatment as to convert the bulk of the alumina into Watersoluble form While avoiding substantial evolution of oxids of sulfur, leaching the calcined material and separating alum from the solution thereby obtained, calcining the alum and thereby converting the same into potassium sulfate, alumina,.and oxids of sulfur, the latter consisting predominately of sulfur trioxid, absorbing the sulfur trioxid by the residue from the alum extraction for.l preparation of aluminum sulfate, extracting and recovering the potassium sulfate, and recovering the residual alumina.

In testimony whereof I afiix my signature.

FRANK K. CAMERON.

l Itns hereby certified that in Letters Patent No. 1,233,977, granted July 17, 191,7,

upon the epplication of Frank Cameron, of Washington, District of Columbia, for an improvement in "Methods of Treating Alunite, en error appears-in the printed specification requiring correction as follows: Page 1, line 69, for the word proposition read proportion; lund that the said Letters Patent should be read with this correction therein thet the same may conform to the record of the case inthe Patent Office. Y

' Sgneii and sealed this 14th dey of August, A. D., 1917.

[sneu] R. F. WHITEHEAD,

Acting Commissioner of Patents. 

